Abstract:

Continuous measurement of respiratory impedance with very high precision
is enabled by executing noise removal. An air vibration pressure by an
oscillation wave obtained by frequency culling such that the oscillation
wave has only frequency components left by the culling from a plurality
of different frequencies, is applied by a loudspeaker 21 to the inside of
an oral cavity. The pressure in the oral cavity is detected and the flow
of breathing is detected. These signals obtained are Fourier-transformed
by a Fourier transforming means 32 and, thereby, a spectrum is obtained.
A breathing high frequency component that contributes as a noise is
obtained by the extracting means 33 using a spectrum that corresponds to
the frequency components culled from the result of the Fourier
transformation. The breathing high frequency component is subtracted from
the spectrum that corresponds to the frequency components left by the
culling and, thereby, the oscillation wave component is extracted. A
computing means 34 executes computation of dividing a pressure component
by a flow component for each frequency for the result of the extraction
and, thereby, the respiratory impedance is obtained.

Claims:

1. A respiratory impedance measuring apparatus comprising:a pressurizing
means to apply an air vibration pressure to an inside of an oral cavity;a
control means that causes the air vibration pressure by an oscillation
wave to be generated, the oscillation wave being a signal that drives the
pressurizing means, the oscillation wave being a signal obtained by
frequency-culling executed such that the signal has only the frequency
components that are left after the culling is executed, from a plurality
of different frequencies;a pressure detecting means that detects a
pressure of the inside of the oral cavity;a flow detecting means that
detects a flow generated by breathing;a Fourier transforming means that
obtains signals obtained by the pressure detecting means and the flow
detecting means under a pressurized condition provided by the
pressurizing means, the Fourier transforming means Fourier-transforming
the signals obtained, the Fourier transforming means obtaining a
spectrum;an extracting means that obtains a breathing high frequency
component based on a spectrum that corresponds to the frequency component
culled from the result of the transformation by the Fourier transforming
means, the extracting means taking out an oscillation wave component by
subtracting the breathing high frequency component from a spectrum that
corresponds to frequency components left by the culling; anda computing
means that divides a pressure component by a flow component for each
frequency for the result of the extraction by the extracting means.

2. The respiratory impedance measuring apparatus of claim 1, whereinthe
control means causes the air vibration pressure by the oscillation wave
having only n/T (n: an integer, T: a real number) frequency components to
be generated by giving a pulse wave having a cycle T as the frequency
culling.

3. The respiratory impedance measuring apparatus of claim 1, whereinthe
control means causes the air vibration pressure by the oscillation wave
to be generated by obtaining the oscillation wave that is
frequency-culled by combining a plurality of sine waves at a plurality of
different frequencies.

4. The respiratory impedance measuring apparatus of any one of claims 1 to
3, whereinthe control means comprises a signal input means that supplies
an input signal to the pressurizing means such that an oscillation wave
having a desired pressure waveform is an output signal, based on reverse
computation using an input signal and an output signal of the
pressurizing means and a transfer function of the pressurizing means.

5. The respiratory impedance measuring apparatus of claim 4, whereinthe
signal input means supplies to the pressurizing means as an input signal
a signal obtained by adding a specific value to each of frequency
components of the signal obtained by the reverse computing, or by reverse
computing the signal formed by adding an impulse to an onset portion of
the output signal.

6. A respiratory impedance measurement method comprising:a pressurizing
step to apply an air vibration pressure to an inside of an oral cavity;a
control step of causing the air vibration pressure by an oscillation wave
to be generated, the oscillation wave being a signal that controls this
pressurizing step, the oscillation wave being a signal obtained by
frequency-culling executed such that the signal has only a plurality of
frequency components that are left after the culling is executed from a
plurality of different frequencies;a pressure detecting step of detecting
a pressure of the inside of the oral cavity;a flow detecting step of
detecting the flow generated by breathing;a Fourier-transforming step of
obtaining signals obtained at the pressure detecting step and the flow
detecting step under the pressurized condition provided at the
pressurizing step, Fourier-transforming the signals obtained, and,
thereby, obtaining a spectrum;an extracting step of obtaining a breathing
high frequency component based on a spectrum that corresponds to the
frequency components culled from the result of the transformation at the
Fourier transforming step, and taking out an oscillation wave component
by subtracting the breathing high frequency component from spectrum that
corresponds to frequency components left by the culling; anda computing
step of dividing a pressure component by a flow component for each
frequency for the result of the extraction at the extracting step,
whereineach of the steps is executed by processing and control of a
computer.

7. The respiratory impedance measurement method of claim 6, whereinat the
control step, the air vibration pressure by an oscillation wave having
only n/T (n: an integer, T: a real number) frequency components is caused
to be generated by supplying a pulse having a cycle T as the
frequency-culling.

8. The respiratory impedance measurement method of claim 6, whereinat the
control step, the air vibration pressure by an oscillation wave is caused
to be generated by obtaining the oscillation wave frequency-culled,
obtained by combining a plurality of sine waves at a plurality of
different frequencies.

9. The respiratory impedance measurement method of any one of claims 6 to
8, whereinthe control step comprises a signal input step of supplying an
input signal at the pressurizing step such that an oscillation wave
having a desired pressure waveform is an output signal, based on reverse
computation using an input signal and an output signal at the
pressurizing step and a transfer function at the pressurizing step.

10. The respiratory impedance measurement method of claim 9, whereinat the
signal input step, a signal is supplied at the pressurizing step, that is
obtained by adding a specific value to each of frequency components of
the signal obtained by the reverse computing, or by reverse computing the
signal formed by adding an impulse to an onset portion of the output
signal.

11. A respiratory impedance display method of executing display on a
displaying apparatus based on respiratory impedance measured by a
respiratory impedance measuring apparatus, whereinthe display is executed
by three-dimensionally taking values based on an impedance axis, a
frequency axis, and a time axis, and whereinan image is created by
including respiratory impedance obtained by executing an interpolation
process for culled frequencies, in an image to execute the display by
three-dimensionally taking values and, thereby, the display is executed.

12. The respiratory impedance display method of claim 11, whereinthe
display is executed by creating an image with the length in the direction
of the time axis, that is taken to be a length enough to repeat therein
at least two sets of exhalation and inhalation.

13. The respiratory impedance display method of claim 11 or 12, whereinthe
display is executed by creating an image that expresses magnitude of an
impedance value using variation in color or variation in gradation.

Description:

TECHNICAL FIELD

[0001]The present invention relates to a respiratory impedance measuring
apparatus and method that are capable of continuously measuring a
respiratory impedance of a human being, etc., and to a respiratory
impedance display method.

BACKGROUND ART

[0002]Conventionally, an apparatus of this kind is known that includes a
sine-wave pressurizing apparatus to apply as a load a sine-wave air
vibration pressure to a respiratory system, an air current velocity
detector to detect an air current velocity of the respiratory system, an
air pressure detector to detect an air pressure of the respiratory
system, and a resistance computing unit that calculates breathing
resistance from the air current velocity and the air pressure detected by
the air current velocity detector and the air pressure detector.

[0003]The conventional apparatus: further includes a reference signal
converter to convert a signal of the sine-wave air vibration pressure
that is applied by the sine-wave pressurizing apparatus into a reference
signal and a vector computing device that processes a signal of the air
current velocity using the reference signal of the sine-wave air
vibration pressure from the reference signal converter and that, thereby,
takes out only a component at the same frequency as that of the reference
signal; and is adapted to calculate the breathing resistance using the
resistance computing unit from the signal of the air current velocity
obtained by the vector computing device and the signal of the air
pressure detected by the air pressure detector.

[0004]As above, this apparatus is adapted to measure the breathing
resistance using the resistance computing unit from the signal of the air
current velocity obtained by the vector computing device and the signal
of the air pressure detected by the air pressure detector and, therefore,
noises may be removed even when the amount of ventilation of the
breathing is a little and the number of ventilating sessions is large.
Therefore the apparatus has an advantage that the apparatus may execute
high precision measurement of breathing resistance (see Patent Document
1).

[0005]However, the removal of the noises is not sufficient even by the
conventional apparatus and realization of a higher-performance
respiratory impedance measuring apparatus is demanded.

[0006]The present invention was conceived in view of the current
circumstances in respiratory impedance measurement and an object thereof
is to provide a respiratory impedance measuring apparatus and method that
are capable of continuously measuring impedance for a plurality of
frequencies at one time. Another object thereof is to provide a
respiratory impedance measuring apparatus and method that are capable of
removing noises and measuring respiratory impedance with extremely high
precision, and a respiratory impedance display method.

Means for Solving the Problems

[0007]The respiratory impedance measuring apparatus according to the
present invention characteristically includes: a pressurizing means to
apply an air vibration pressure to the inside of an oral cavity, a
control means that causes the air vibration pressure to be generated, by
an oscillation wave that is a signal to drive this pressurizing means and
that is a signal obtained by frequency-culling executed such that the
signal has only the frequency components that are left after the culling
is executed from a plurality of different frequencies; a pressure
detecting means that detects the pressure of the inside of an oral
cavity; a flow detecting means that detects a flow generated by
breathing; a Fourier transforming means that obtains signals obtained by
the pressure detecting means and the flow detecting means under the
pressurized condition provided by the pressurizing means, that
Fourier-transforms the signals obtained, and that obtains a spectrum; an
extracting means that obtains a breathing high frequency component based
on a spectrum that corresponds to the frequency component culled from the
result of the transformation by the Fourier transforming means, and that
takes out an oscillation wave component by subtracting the breathing high
frequency component from a spectrum that corresponds to a frequency
component left by the culling; and a computing means that divides a
pressure component by a flow component for each frequency for the result
of the extraction by the extracting means.

[0008]The respiratory impedance measuring apparatus according to the
present invention is characterized in that the control means causes the
air vibration pressure to be generated, by the oscillation wave having
only n/T (n: an integer, T: a real number) frequency components, by
giving a pulse wave having the cycle T as the frequency culling. Such
frequency-culling is referred to as <frequency-culling 1>. In
<frequency-culling 1>, when T is determined, a plurality of
frequency components are obtained that are left by culling the frequency
components other than n/T (n: an integer) frequency components.

[0009]The respiratory impedance measuring apparatus according to the
present invention is characterized in that the control means combines a
plurality of sine waves at different frequencies, thereby, obtains an
oscillation wave frequency-culled, and causes the air vibration pressure
by the oscillation wave to be generated. Such frequency-culling is
referred to as <frequency-culling 2>. In <frequency-culling
2>, the signal is also enabled to have only a plurality of
integer-frequency components left by culling desired integers from
consecutive integers and, therefore, the signal may include a plurality
of integer-frequency components left by culling odd-number frequency
components.

[0010]The respiratory impedance measuring apparatus according to the
present invention is characterized in that the control means includes a
signal input means that supplies an input signal to the pressurizing
means such that an oscillation wave having a desired pressure waveform is
an output signal, based on reverse computation using the input signal and
the output signal of the pressurizing means and a transfer function of
the pressurizing means.

[0011]The respiratory impedance measuring apparatus according to the
present invention is characterized in that the signal input means
supplies to the pressurizing means as an input signal a signal obtained
by adding a specific value to each of frequency components of the signal
obtained by the reverse computing, or by reverse computing the signal
formed by adding an impulse to an onset portion of the output signal.

[0012]The respiratory impedance measurement method according to the
present invention characteristically includes: a pressurizing step to
apply an air vibration pressure to the inside of an oral cavity; a
control step of causing the air vibration pressure to be generated, by an
oscillation wave that is a signal to control this pressurizing step and
that is a signal obtained by frequency-culling executed such that this
signal has only the frequency component that is left after the culling is
executed from a plurality of different frequencies; a pressure detecting
step of detecting the pressure of the inside of the oral cavity; a flow
detecting step of detecting the flow generated by breathing; a
Fourier-transforming step of obtaining signals obtained at the pressure
detecting step and the flow detecting step under the pressurized
condition provided at the pressurizing step, Fourier-transforming the
signals obtained, and, thereby, obtaining a spectrum; an extracting step
of obtaining a breathing high frequency component based on a spectrum
that corresponds to the frequency components culled from the result of
the transformation at the Fourier transforming step, and taking out an
oscillation wave component by subtracting the breathing high frequency
component from a spectrum that corresponds to frequency components left
by the culling; and a computing step of dividing a pressure component by
a flow component for each of frequencies for the result of the extraction
at the extracting step, and the method is characterized in that each of
the steps is executed by processing and control of a computer.

[0013]The respiratory impedance measurement method according to the
present invention is characterized in that, at the control step, the air
vibration pressure is caused to be generated, by an oscillation wave
having only n/T (n: an integer, T: a real number) frequency components by
supplying a pulse wave having a cycle T as the frequency-culling. Such
frequency-culling is <frequency-culling 1>.

[0014]The respiratory impedance measurement method according to the
present invention is characterized in that, at the control step, the air
vibration pressure is caused to be generated, by an oscillation wave by
obtaining the oscillation wave frequency-culled, that is obtained by
combining a plurality of sine waves at a plurality of different
frequencies. Such frequency-culling is <frequency-culling 2>.

[0015]The respiratory impedance measurement method according to the
present invention is characterized in that the control step includes a
signal input step of supplying an input signal at the pressurizing step
such that an oscillation wave having a desired pressure waveform is an
output signal, based on reverse computation using the input signal and
the output signal at the pressurizing step and a transfer function at the
pressurizing step.

[0016]The respiratory impedance measurement method according to the
present invention is characterized in that, at the signal input step, a
signal is supplied at the pressurizing step, that is obtained by adding a
specific value to each of frequency components of the signal obtained by
the reverse computing, or by reverse computing the signal formed by
adding an impulse to an onset portion of the output signal.

[0017]The respiratory impedance display method according to the present
invention is characterized in that, in a respiratory impedance display
method of executing display on a displaying apparatus based on the
respiratory impedance measured by the respiratory impedance measuring
apparatus: the display is executed by three-dimensionally taking values
based on an impedance axis, a frequency axis, and a time axis; an image
is created by including respiratory impedance obtained by executing an
interpolation process for the culled frequencies, in the display to
execute the display by three-dimensionally taking values; and, thereby,
the display is executed.

[0018]The respiratory impedance display method according to the present
invention is characterized in that the display is executed by creating
the image with the length in the direction of the time axis, that is
taken to be a length enough to repeat therein at least two sets of
exhalation and inhalation.

[0019]The respiratory impedance display method according to the present
invention is characterized in that the display is executed by creating an
image that expresses magnitude of an impedance value using variation in
color or variation in gradation.

EFFECTS OF THE INVENTION

[0020]According to the present invention: an air vibration pressure by an
oscillation wave that is frequency-culled is applied to the inside of an
oral cavity; the pressure of the inside of the oral cavity is detected;
the flow of breathing is detected; a spectrum is obtained by
Fourier-transforming these signals obtained; a breathing high frequency
component that contributes as a noise is obtained using a spectrum that
corresponds to frequency components culled from the result of the Fourier
transformation; the breathing high frequency component is subtracted from
a spectrum that corresponds to the frequency components left by the
culling; thereby, an oscillation wave component is extracted; computing
is executed of dividing a pressure component by a flow component for each
of frequencies for the result of this extraction; and, thereby,
respiratory impedance is obtained. Therefore, the respiratory impedance
may be obtained using the oscillation wave component from which the
breathing high frequency component is securely removed and, therefore,
impedance measurement with extremely high precision may be enabled.

[0021]According to the present invention: the air vibration pressure by
the oscillation wave having only the n/T (n: an integer, T: a real
number)frequency components is caused to be generated by supplying the
pulse having the cycle T; therefore, the breathing high frequency
component is obtained using the spectrum that corresponds to the
frequency components culled; and the breathing high frequency component
is subtracted from the spectrum that corresponds to the frequency
components left by the culling. Therefore, the breathing high frequency
component may securely be removed and the respiratory impedance
measurement with extremely high precision is enabled.

[0022]According to the present invention, the plurality of sine waves at
the plurality of different frequencies are combined and, thereby, the air
vibration pressure by the oscillation wave that is
frequency-component-culled is caused to be generated. Therefore, only the
breathing high frequency component is included by the spectrum that
corresponds to the frequency components culled and, therefore, the
breathing high frequency component may securely be removed and the
respiratory impedance measurement with extremely high precision is
enabled.

[0023]According to the present invention, an input signal is supplied to a
pressurizing executing portion such that the oscillation wave having a
desired pressure waveform is the output signal based on the reverse
computation using the input signal and the output signal for the
pressurizing and a transfer function of the pressurizing executing
portion. Therefore, the measurement may be executed using the oscillation
wave having the desired pressure waveform and respiratory impedance
measurement with extremely high precision is enabled.

[0024]According to the present invention, the input signal is the signal
obtained by adding a specific value to each of the frequency components
of the signal obtained by the reverse computing, or by reverse computing
the signal formed by adding an impulse to the onset portion of the output
signal. Therefore, the signal waveform of the result of the reverse
computing may be stabilized and, thereby, the measurement using the
oscillation wave having a desired waveform may be executed and the
respiratory impedance measurement with extremely high precision is
enabled.

[0025]According to the respiratory impedance display method according to
the present invention, in the respiratory impedance display method of
executing display on a displaying apparatus based on the respiratory
impedance measured by the respiratory impedance measuring apparatus: the
display is executed three-dimensionally taking values based on the
impedance axis, the frequency axis, and the time axis; an image is
created by including the respiratory impedance obtained by executing an
interpolation process for the culled frequencies, in the display to
execute display three-dimensionally taking values; and, thereby, the
display is executed. Therefore, the result of the interpolation process
is also displayed as an image. Therefore, variation of the impedance
value may minutely and smoothly be displayed and grasp of the impedance
for the whole frequencies may properly be executed.

[0026]According to the respiratory impedance display method according to
the present invention, the display is executed by creating the image with
the length in the direction of the time axis that is a length long enough
to repeat therein at least two sets of exhalation and inhalation.
Therefore, not an observation of a sudden variation but an observation
having a specific span is enabled and, thereby, proper observations may
be secured.

[0027]According to the respiratory impedance display method according to
the present invention, the display is executed by creating the image that
expresses magnitude of an impedance value using variation in color or
variation in gradation. Therefore, to obviously distinguish the
magnitudes of impedance values is easily enabled and it is expected that
the method is very useful for various researches and inspections that use
the respiratory impedance.

BEST MODES FOR CARRYING OUT THE INVENTION

[0028]Embodiments of a respiratory impedance measuring apparatus and
method according to the present invention will be described with
reference to the accompanying drawings. FIG. 1 is a diagram of the
configuration of the embodiment of the respiratory impedance measuring
apparatus according to the present invention. The respiratory impedance
measuring apparatus includes as its main components: a tube 11 whose tip
is attached to an oral cavity of a human and through which a breathing
flow flows; a pressure sensor 12 that is attached to the tube 11 and that
makes up a pressure detecting means to detect the pressure in the oral
cavity; a flow sensor 13 that makes up a flow detecting means of
detecting the flow of breathing at the same position as that of the
pressure sensor 12; a loudspeaker 21 that makes up a pressurizing means
to apply an air vibration pressure to the inside of the oral cavity; and
a computer 30.

[0029]An output signal of the pressure sensor 12 is amplified by an
amplifier 14, is digitized by an A/D converter 15, and is taken in by the
computer 30. An output signal of the flow sensor 13 is amplified by an
amplifier 16, is digitized by an A/D converter 17, and is taken in by the
computer 30.

[0030]The computer 30 includes a control means 31, a Fourier transforming
means 32, an extracting means 33, and a computing means 34. The control
means 31 includes a signal input means 35. The control means 31 outputs a
signal driving the loudspeaker 21 that is the pressurizing means and
causes the air vibration pressure by an oscillation wave having only
odd-number frequency components or even-number frequency components, to
be generated. An output of the control means 31 is converted into an
analog signal by a D/A converter 22 and is sent to a driver 23. The
driver 23 drives the loudspeaker 21 and, thereby, the air vibration
pressure is applied to the inside of the oral cavity.

[0031]In the above, the control means 31 causes the air vibration pressure
by the oscillation wave having n/T (n: an integer, T: a real number)
frequency components, to be generated by giving a pulse wave having the
cycle of T second (<frequency-culling 1>). Though various waveforms
may be considered as the pulse wave, for example, as depicted in FIG.
2(a), a triangular pulse has the temporal width of about 25 ms at the
base level. When this triangular pulse is output with the cycle T that
is, for example, T=0.5 second, a triangular pulse wave having a spectrum
of 2, 4, 6, 8 Hz, . . . may be given (FIG. 2(b)). When the triangular
pulse is output with the cycle T that is, for example, T=0.333 second, a
triangular pulse wave having a spectrum of 3, 6, 9, 12 Hz, . . . may be
given.

[0032]As depicted in FIG. 3, a Hanning pulse as another example has the
temporal width of about 25 ms at the base level. A pulse wave using this
pulse is created and output similarly to the case of the triangular pulse
wave.

[0033]The control means 31 causes the air vibration pressure by an
oscillation wave having only desired real-number frequency components, to
be generated by giving a wave obtained by combining a plurality of sine
waves at a plurality of different frequencies (<frequency-culling
2>). In this case, a signal depicted in FIG. 4 that is a noise wave is
output. In this case, a noise wave having only even-number frequency
components is obtained by combining sine waves having even-number
frequencies such as, for example, 2, 4, 6, . . . , 34 Hz. A noise wave
having only odd-number frequency components is obtained by combining sine
waves having odd-number frequencies such as, for example, 1, 3, 5, . . .
, 33 Hz. A noise is realized by randomizing the phase of each the sine
waves.

[0034]The signal input means 35 included in the control means 31 supplies
an input signal to the loudspeaker 21 such that an oscillation wave
having a desired waveform is an output signal, based on reverse computing
using an input signal and an output signal of the loudspeaker 21, and a
transfer function of the loudspeaker 21.

[0035]More specifically, describing using, for example, a triangular
pulse, when the loudspeaker 21 is driven by inputting thereinto a
triangular pulse as depicted in FIG. 5(a), an output signal of the
loudspeaker 21 becomes a signal having a local maximum point on each of
the upper and the lower sides of the zero level as depicted in FIG. 5(b).
A model as depicted in FIG. 5(c) is considered. Representing the transfer
function of the loudspeaker 21 as "H(ω)", the input signal thereof
as "X(ω)", and the output signal thereof as "Y(ω)", the
following holds and, therefore, x' (t) is obtained by reverse computation
and is used as a driving signal.

[0037]Y(ω) obtained has no component that includes frequencies up to
a high frequency and, therefore, x'(t) obtained from (Equation 1) is
unstable. Therefore, as expressed in (Equation 2), a term obtained by
adding a constant "A0" to the denominator of X'(ω) is
inversely Fourier-transformed and, thereby, x'(t) is obtained and is used
as the driving signal. The signal x'(t) depicted in FIG. 5(e) may also be
obtained by reverse-computing a signal formed by adding an impulse to an
onset portion as depicted in FIG. 5(d) of an output signal of the
loudspeaker 21 as depicted in FIG. 5(b).

[0038]Though the case for the triangular pulse is described in the above,
as to a Hanning pulse, a signal may also be obtained by the reverse
computation and this signal may also drive the loudspeaker 21. As to a
sine wave, a signal may also be obtained by the reverse computation and a
noise wave may also be obtained by this signal combining.

[0039]As to which one of the pulse wave, the noise wave, and the sine wave
having a single frequency is used, an instruction may be given to the
computer 30 using a keyboard, etc., not depicted and, in response to
this, the control means 31 outputs a signal waveform selected thereby.

[0040]The Fourier transforming means 32, the extracting means 33, and the
computing means 34 included in the computer 30 will be described. Under
the pressurized condition in the oral cavity caused by a driving of the
loudspeaker 21 as above, the Fourier transforming means 32 obtains
signals using the pressure sensor 12 and the flow sensor 13,
Fourier-transforms these signals obtained, and obtains a spectrum. A CIC
filter 36 is provided in the pre-stage of the Fourier transforming means
32 and separates a breathing signal and an oscillation component obtained
by the pressure sensor 12 and the flow sensor 13 from each other. The
Fourier transforming means 32 takes out a signal using a Hanning window
before the processing when necessary.

[0041]The extracting means 33 obtains a breathing high frequency component
using the spectrum that corresponds to the frequency components culled
from the result of the transformation by the Fourier transforming means
32, and takes out the oscillation wave component by subtracting the
breathing high frequency component from the spectrum that corresponds to
the frequency components left by the culling. Describing based on
<frequency-culling 1>, as to the spectrum obtained by the Fourier
transforming means 32, the breathing high frequency component is obtained
using the spectrum that corresponds to other frequencies excluding n/T
(n: an integer) frequency components, and the oscillation wave component
is taken out by subtracting the breathing high frequency component from
the spectrum that corresponds to the frequency components left by the
culling (n/T-frequency components).

[0042]Describing based on <frequency-culling 2>, as to the spectrum
obtained by the Fourier transforming means 32, the extracting means 33
obtains the breathing high frequency component using the spectrum that
corresponds to the frequency components (odd-number frequency components
or even-number frequency components) that are different from the
frequency components (in this case, even-number frequency components or
odd-number frequency components) given to the loudspeaker 21, and takes
out the oscillation wave component by subtracting the breathing high
frequency component from the spectrum that corresponds to the frequency
components given to the loudspeaker 21.

[0043]As to the result of the extraction by the extracting means 33, the
computing means 34 calculates respiratory impedance by dividing a
pressure component by a flow component for each frequency. Representing
the respiratory impedance as Z(ω), an oscillation wave component of
the pressure in the oral cavity as P(ω), and an oscillation wave
component of the flow as F(ω) and assuming that the respiratory
impedance Z(ω) includes a resistance component R(ω) and a
reactance component X(ω), the respiratory impedance Z(ω) is
obtained using the following equations.

[0044]The respiratory impedance Z(ω) obtained by the computing means
34 is converted into a display signal for a displaying unit 40 such as an
LCD that is connected to the computer 30 and is output to the displaying
unit 40 and, thereby, display is executed.

[0045]Operations by the respiratory impedance measuring apparatus
configured as above will be described. In this example, the triangular
pulse wave is selected and a measuring operation is started. The
loudspeaker 21 is driven with the cycle of T second (for example, at
intervals of 0.5 second) by the control means 31 and the signal input
means 35 using the waveform obtained by the reverse computation.

[0046]At this time, both of the waveforms of the signals obtained by the
pressure sensor 12 and the flow sensor 13 each are a waveform formed by
superimposing the triangular pulse wave on the breathing signal as
depicted in FIG. 6(a). This waveform is passed through the CIC filter 36
and the separation of the breathing wave and the oscillation wave (the
triangular pulse wave) from each other is executed. FIG. 7 depicts the
frequency property of the CIC filter 36. The CIC filter 36 may execute
the separation without any shift of the phase. However, the breathing
signal includes a high frequency component (the same frequency band as
that of the oscillation signal) and, therefore, the separation may not be
completely executed.

[0047]After the separation by the CIC filter 36, as depicted in FIG. 6(b),
as to the oscillation wave, a section of one second is taken out at the
intermediate point between two triangular pulses and is used for signal
processing. As depicted in FIG. 8, a section of T second is taken out and
a process using a Hanning window is executed for each pulse and, thereby,
pulses are taken out.

[0048]Following the process using the Hanning window, Fourier
transformation by the Fourier transforming means 32 is executed and a
spectrum is obtained. At this time, as to the spectrum obtained, for
example, when a pulse is driven with the cycle of 0.5 second, as depicted
in FIG. 9, the breathing signal spectrum is obtained that includes no
oscillation wave component in its spectrum of odd-number frequencies of
1, 3, 5, . . . that correspond to the frequency components culled. The
spectrum of even-number frequencies of 2, 4, 6, . . . that corresponds to
the frequency components left by the culling includes the oscillation
wave component and the breathing signal component.

[0049]As depicted in FIG. 10, the extracting means 33 subtracts a noise
component that is estimated from the spectrum of the odd-number
frequencies, from the spectrum of the even-number frequencies and,
thereby, takes out the oscillation wave component.

[0050]The breathing high frequency signal that is equal to or higher than
3 Hz and that is conventionally considered not to be included in the
breathing signal, is removed by the processing of the extracting means 33
and, therefore, high precision respiratory impedance measurement is
enabled. The computing means 34 divides the pressure component by the
flow component and, thereby, calculates the respiratory impedance as
expressed by Equation (2) for each frequency for the result of the
extraction by the extracting means 33. A display signal of the
respiratory impedance calculated is created and is output to the
displaying unit 40 and, thereby, display is executed.

[0051]The respiratory impedance that is measured and displayed as above is
depicted in FIG. 11. FIG. 12 depicts the respiratory impedance obtained
when the breathing high frequency the removal of the breathing high
frequency signal is not executed. In each of FIGS. 11 and 12, the axis of
abscissa is a frequency axis whose one section of graduation corresponds
to 1 Hz and the axis of ordinate represents the impedance. An oblique
axis is the time axis. A genuine resistance portion is displayed in the
upper portion of the diagram and a reactance portion is displayed in the
lower portion of the diagram. In this case, by consecutively giving the
triangular pulses at intervals of 0.5 second, display of new impedance
appears one after another and the display is updated. Thereby, continuous
measurement of the impedance is executed. As apparently seen from FIGS.
11 and 12, it is understood that the noise is removed and high precision
respiratory impedance measurement is enabled. As apparent from the
subtracting process by the extracting means 33, the component left by the
subtraction is the even-number-frequency component of 2, 4, 6, . . . that
corresponds to the frequency component left by the culling and, the
odd-number-frequency component of 1, 3, 5, . . . that corresponds to the
frequency component culled is not present. The computing means 34
executes an interpolating process and, thereby, respiratory impedance
measurement is enabled for the component that is not present.

[0052]The case where the noise wave is selected instead of the triangular
pulse wave and the measuring operation is started (<frequency-culling
2>) will be described. The loudspeaker 21 is driven by the control
means 31 and the signal input means 35 using the noise wave having only
even-number-frequency component based on the waveform obtained by the
combining. At this time, both of the waveforms of the signals obtained by
the pressure sensor 12 and the flow sensor 13 each are a waveform formed
by superimposing the noise wave on the breathing signal as depicted in
FIG. 13(a). These signals are passed through the CIC filter 36 and,
thereby, the separation of the breathing wave and the oscillation wave
(noise wave) from each other is executed (FIG. 13(b)).

[0053]After the separation by the CIC filter 36, as depicted in FIG.
14(a), as to the oscillation wave, a section of one second is taken out
and is used for the signal processing. As depicted in FIG. 14(b), Fourier
transformation by the Fourier transforming means 32 is executed for the
noise wave from which the section of one second is taken out and,
thereby, the spectrum is obtained.

[0054]As to the spectrum obtained by the Fourier transformation, the
loudspeaker 21 is driven by the noise wave having only the
even-number-frequency component combined by the control means 31 and the
signal input means 35. Therefore, a breathing signal spectrum is obtained
whose spectrum of the odd-number frequencies of 1, 3, 5, . . . that
corresponds to the frequency components culled does not include the
oscillation wave component. The spectrum of the even-number frequencies
of 2, 4, 6, . . . that corresponds to the frequency components left by
the culling includes the oscillation wave component and the breathing
signal component.

[0055]The extracting means 33 executes subtraction of the
odd-number-frequency spectrum from the even-number-frequency spectrum
and, thereby, takes out the oscillation wave component. The processes
after this are same as the processes executed when the triangular pulse
wave is used (FIGS. 9 and 10 and the computation using Equation (2)). A
display signal of the respiratory impedance calculated is created and is
output to the displaying unit 40, and, thereby, display is executed. When
the noise wave is used as above, the noise may also be removed and high
precision respiratory impedance measurement is enabled. By continuously
giving the noise wave, new impedance display appears one after another
and, thereby, the display is updated. Thereby, continuous measurement of
the impedance is executed. When the noise wave is used, display whose
noise is removed is executed similarly to the case depicted in FIG. 11
and the continuous measurement of the impedance is enabled.

[0056]In the embodiment of the present invention, the computing means 34
creates the image to execute the display on the displaying apparatus and
executes the display and, thereby, a respiratory impedance display method
is realized. As to the respiratory impedance calculated by the computing
means 34, the computing means 34, for example: determines a coordinate
such that each frequency value is taken from the side distant from a
viewer to the side close thereto of the image; takes out a resistance
component Rrs for each frequency; plots this in the direction of the
height of the screen of the displaying apparatus; takes the measurement
time in the rightward direction of the screen; creates a
three-dimensional image as depicted in FIG. 15; and displays the
three-dimensional image on the displaying apparatus. This display is
executed three-dimensionally taking values using the impedance axis, the
frequency axis, and the time axis.

[0057]For creating the image, an image is created and is displayed that is
formed by including the respiratory impedance obtained by executing the
interpolation process for the frequencies culled, in the case where
values are three-dimensionally taken. For example, when the odd-number
frequencies are culled, two impedance values are already obtained that
correspond to even-number frequencies that are adjacent to an odd number
culled. Therefore, the average of these two impedance values is obtained
and is used as an impedance value that corresponds to the frequency
culled. In this manner, the result of the interpolation process is also
converted into an image and is displayed as the image and, therefore,
variation of the impedance value may minutely and smoothly be displayed
and grasp of the impedance for the whole frequencies may properly be
executed.

[0058]The sampling time is 0.5 second and, as depicted in FIG. 15(b), the
image is created and displayed taking the length in the direction of the
time axis that is a length long enough to repeat therein at least two
sets of exhalation and inhalation. In the example of FIG. 15, the length
is taken to be long enough to repeat therein three sets of exhalation and
inhalation.

[0059]An image is also created and displayed that expresses the magnitude
of the impedance value using variation in color or variation in
gradation. In FIG. 15, an image is created and displayed being colored
for the resistance value Rrs based on the color scale presented in the
lower portion of FIG. 15.

[0060]Images obtained by the processes are displayed and, therefore, a
subject only has to repeat inhaling and exhaling and images as depicted
in FIG. 15 may automatically and time-sequentially be created and
displayed. Each of the images may visually be observed as an image that
expresses the variation of the respiratory impedance using variation in
color or variation in gradation, including the portions that correspond
to the frequencies culled.

[0061]Therefore, as apparently seen from the variation of the respiratory
impedance of a 66-year-old healthy person depicted in FIG. 15(a) and the
variation of the respiratory impedance of a 65-year-old COPD (chronic
obstructive pulmonary disease) patient depicted in FIG. 15(b), to
visually and obviously distinguish a non-healthy person and a healthy
person from each other is easily enabled and it is expected that the
method is very useful for various researches and inspections that use
respiratory impedance. "% FEV1" of FIG. 15(b) is a value that indicates
how many % of the forced vital capacity is exhaled in one second.
Therefore, in this example, it is presented that 24.4% was able to be
exhaled in one second.

BRIEF DESCRIPTION OF DRAWINGS

[0062]FIG. 1 is a diagram of the configuration of a respiratory impedance
measuring apparatus according to an embodiment of the present invention.

[0063]FIG. 2 is a diagram of an example of a triangular pulse wave that is
an oscillation wave used in the respiratory impedance measuring apparatus
according to the embodiment of the present invention.

[0064]FIG. 3 is a diagram of an example of a Hanning pulse wave that is an
oscillation wave used in the respiratory impedance measuring apparatus
according to the embodiment of the present invention.

[0065]FIG. 4 is a diagram of an example of a noise wave that is an
oscillation wave used in the respiratory impedance measuring apparatus
according to the embodiment of the present invention.

[0066]FIG. 5 is a diagram for explaining the process of creating, using
reverse computation, the oscillation wave used in the respiratory
impedance measuring apparatus according to the embodiment of the present
invention.

[0067]FIG. 6 is a diagram of a process of obtaining the respiratory
impedance using the triangular pulse wave that is the oscillation wave by
the respiratory impedance measuring apparatus according to the embodiment
of the present invention.

[0068]FIG. 7 is a diagram of the frequency property of a filter employed
in the respiratory impedance measuring apparatus according to the
embodiment of the present invention.

[0069]FIG. 8 is a diagram of a process of obtaining the respiratory
impedance using the triangular pulse wave that is the oscillation wave by
the respiratory impedance measuring apparatus according to the embodiment
of the present invention.

[0070]FIG. 9 is a diagram of a process of obtaining the respiratory
impedance using the triangular pulse wave that is the oscillation wave by
the respiratory impedance measuring apparatus according to the embodiment
of the present invention.

[0071]FIG. 10 is a diagram of a process of obtaining the respiratory
impedance using the triangular pulse wave that is the oscillation wave by
the respiratory impedance measuring apparatus according to the embodiment
of the present invention.

[0072]FIG. 11 is a diagram of the respiratory impedance obtained by the
respiratory impedance measuring apparatus according to the embodiment of
the present invention.

[0073]FIG. 12 is a diagram of respiratory impedance obtained by a
respiratory impedance measuring apparatus that does not use the approach
of the present invention.

[0074]FIG. 13 is a diagram of a process of obtaining the respiratory
impedance using a noise wave that is the oscillation wave by the
respiratory impedance measuring apparatus according to the embodiment of
the present invention.

[0075]FIG. 14 is a diagram of a process of obtaining the respiratory
impedance using a noise wave that is the oscillation wave by the
respiratory impedance measuring apparatus according to the embodiment of
the present invention.

[0076]FIG. 15 is a diagram of an example of respiratory impedance for each
of a healthy person and a non-healthy person displayed using the
respiratory impedance measuring apparatus according to the embodiment of
the present invention.